Can Graves' Disease Cause Unilateral Thyroid Lobe Enlargement?
Yes, Graves' disease can cause unilateral thyroid lobe enlargement, though this presentation is uncommon since the disease typically involves the entire thyroid gland diffusely and symmetrically. 1
Typical Presentation Pattern
Graves' disease classically presents with diffuse, symmetric thyroid enlargement (goiter) affecting the entire gland. 2, 3 The ACR Appropriateness Criteria explicitly states that goiter enlargement "can involve the whole gland symmetrically or predominantly affect one lobe." 1
Evidence for Unilateral Involvement
A documented case report demonstrates that Graves' disease can present with strictly unilateral involvement. 4 In this case:
- A 31-year-old female presented with unilateral goiter and hyperthyroidism 4
- High-resolution ultrasonography showed autoimmune thyroid disease morphology limited only to the right lobe 4
- I-123 scintigraphy revealed several-fold increased uptake in the right lobe only, while the left lobe showed normal uptake 4
- Fine needle aspiration cytology of the right lobe showed inflammatory infiltrate with lymphocytes, absent in the left lobe 4
- TSH receptor antibodies and thyroid peroxidase antibodies were significantly elevated 4
Clinical Implications and Diagnostic Approach
When encountering asymmetric or unilateral thyroid enlargement with thyrotoxicosis:
- Measure TSH receptor antibodies to confirm Graves' disease, as this is the primary diagnostic test 1, 3
- Perform thyroid ultrasonography to characterize the morphology and extent of involvement 2, 3
- Consider radioiodine uptake and scan in ambiguous cases to confirm the diagnosis and assess functional activity of each lobe 1
- Evaluate for nodules that may require biopsy, as asymmetric enlargement can also suggest toxic adenoma or toxic multinodular goiter 1
Important Caveats
While unilateral Graves' disease is possible, asymmetric thyroid enlargement should prompt consideration of alternative diagnoses including toxic adenoma, toxic multinodular goiter, or even malignancy. 1 The differential diagnosis becomes particularly important because these conditions have different treatment implications and prognoses compared to classic Graves' disease. 5
Doppler ultrasound can help differentiate between overactive thyroid conditions (showing increased blood flow) versus destructive thyroiditis (showing decreased blood flow), though radionuclide uptake studies remain the gold standard for directly measuring thyroid activity. 1